I don't care what state you're in. If you're married, your x just can't legally take your child. Period. Unless she kidnaps him or her. If that's the case you'll have to file an order against her. If she doesn't let you see him or her you can even call the police. It's against the law. You should get letters of recomendation from anyone who will give you a good word, prove you're going to support the child in some way, show you're not a danger to the child in anyway by not having past police records, prove you have good credit, no accidents, etc.....what ever it takes, if there's going to be a fight.
If married, you should file devorce proceedings, you'll have the upper hand by requesting patial custudy. She will most likey give it to you because if she doesn't, she's going to have a fight and pay for more attorney fees. The judge will side with you. Blood issue or not you're still his or her father and the court wants the father to be involved unless he's a career criminal or drug addict.
If not married. You will have still file a court action. If she denies you're the father. Then a blood test will have to be arranges by order of the court. If she admits your the father, then, you should have letters of recomendation, by anyone, who will put in a good word for you as well as show you're going to contibute finacially to the child, etc.